A surface-mounted light-emitting device on which light-emitting elements, such as a light-emitting diode (LED) and a laser diode (LD), are mounted has a large number of advantages in that color reproduction of light with high-intensity light excellent in visibility can be achieved, the size thereof can be reduced, the power consumption is low, and long-life is achieved. Therefore, the surface-mounted light-emitting device is used as lighting devices, such as electric bulbs, downlights, base lights, streetlights, and signals, back light sources of liquid crystal displays and the like, and the like, for example, and the use thereof has rapidly expanded.
A typical surface-mounted light-emitting device has a lead frame in which a pair of leads are disposed in such a manner as to be separated from each other, a molded resin body having a concave portion to which the lead frame is exposed at the bottom portion and an insulation portion which insulates the pair of leads, a light-emitting element mounted on the lead frame exposed to the bottom portion of the concave portion and connected to the pair of leads in such a manner that electricity can be conducted therebetween, and a transparent resin layer formed by filling the concave portion with a transparent resin, for example (Patent Documents 1 and 2). Herein, the molded resin body has a function of protecting the light-emitting element and reflecting light emitted from the light-emitting element to the front of the light-emitting device to increase the luminance.
When such a surface-mounted light-emitting device is disposed in such a manner that the light-emitting element faces upward in a perpendicular direction, the light emitted downward from the light-emitting element enters the surface of the lead frame exposed to the bottom portion of the concave portion, and the light in the transverse direction (horizontal direction) emitted from the light-emitting element enters the inner wall surface of the concave portion of the molded resin body. In order to reflect the light entering from the light-emitting element to the front to increase the luminance, an increase in the optical reflectance of the surface of the lead frame and the surface of the molded resin body (hereinafter referred to as “optical reflectance”) has been demanded. Therefore, for example, an Ag plating layer is formed as a reflective film on the lead frame surface.
Herein, since Ag used as the plating layer on the lead frame surface shows the highest optical reflectance among metals, Ag is suitable as the material of the reflective film in order to reflect much light. However, Ag has a problem in that Ag reacts with halogen ion and sulfur contained in the atmosphere or sealing resin to generate substances which discolor the reflective film surface into dark brown, such as halides, e.g., chlorides (AgCl) and sulfides (Ag2S), with the progress of the operation time of the surface-mounted light-emitting device, so that the optical reflectance is reduced. Moreover, Ag has a characteristic of aggregating due to the heat generated from the light-emitting element. Also due to the characteristic, Ag has a problem of reducing the optical reflectance.
In order to solve the problems, Patent Document 3 discloses a lead frame in which silicone resin is used for sealing resin and a pure Ag plating layer on a reflective surface is further coated with an Ag—Au alloy plating layer which is difficult to form chlorides and sulfides, for example. However, since the Ag—Au alloy plating layer contains an alloy containing Au in which the Ag content is limited to less than 50 mass % as the main component, the formation operation thereof is complicated. Further, since the thickness is 0.1 μm or more and 0.6 μm or less, the cost also becomes high.
On the other hand, the surface-mounted light-emitting device is manufactured by transfer molding using thermosetting resin as a resin material which gives a molded resin body, for example. More specifically, the surface-mounted light-emitting device is manufactured using a mold having an upper mold having an upper mating surface in which a concave portion corresponding to the three dimensional shape of the molded resin body is formed at a predetermined position, a lower mold having a flat lower mating surface, and a resin injection hole by a method including following (a) to (f) processes (Patent Documents 1 and 4).
(a) Process of holding and fixing the lead frame by the upper mating surface and the lower mating surface.
(b) Process of injecting liquid thermosetting resin into the internal space formed with the concave portion of the upper mating surface and the lead frame and/or the lower mating surface from the resin injection hole.
(c) Process of heating a mold to cure the injected liquid thermosetting resin, and then bonding the cured resin body to a predetermined position of the lead frame.
(d) Process of removing the same from the mold to thereby obtain a molded resin body in which the lead frame and the cured resin body are integrally formed and which has a concave portion to which the lead frame is exposed at the bottom portion.
(e) Process of mounting a light-emitting element on the lead frame exposed to the bottom portion of the concave portion in such a manner that electricity can be conducted therebetween.
(f) Process of filling the concave portion with transparent resin to seal the light-emitting element.
According to the above-described former manufacturing method, an advantage that a large number of surface-mounted light-emitting devices can be manufactured at once is obtained by utilizing the transfer molding. However, in the mold release process of (d), the mold releasability of the molded resin body from the mold is very poor, and therefore there is a problem in that the deformation of the molded resin body is likely to occur and, depending on circumstances, the cohesive failure occurs, so that the molded resin body is broken. Therefore, in the former manufacturing method, the defective product ratio sometimes becomes very high.
Furthermore, in the above-described former manufacturing method, there is a problem in that chipping occurs in the molded resin body in a portion where the molded resin body having the concave portion and the lead frame contact each other and a resin burr is formed at the bottom portion of the concave portion of the molded resin body, so that the product yield decreases.